532 TRANSFORMATION OF ENERGY 



LECTURE XLII 



AUTONOMOUS LOCOMOTORY MOVEMENTS 



Having discussed the movements exhibited exclusively by fixed plants, 

 we must now turn to movements in those plants or plant parts which are capable 

 of locomotion from place to place. At the first glance it would appear as if we 

 had to deal in such cases with an entirely different category of phenomena from 

 those we have hitherto been considering. More careful study leads us, however, 

 to the conclusion that it is only the nature of the reactions, i. e. the change of 

 place and the apparatus by which these reactions are carried out, that alone are 

 novel. The general and special conditions under which locomotion is effected 

 are on the contrary essentially similar to those we have met with already in the 

 phenomena of growth and movement in fixed plants^ The external stimuli 

 which influence the nature of the response are precisely the same immaterial and 

 material agents referred to in previous lectures on movements in the higher 

 plants. Indeed many authors have advocated the treatment of locomotory 

 movements simultaneously with those of curvature. While keeping these two 

 series of phenomena apart in our present discussion on the subject, attention 

 must be drawn to the numerous analogies which exist between them, further 

 instances of which we shall meet with frequently enough later on. 



We will first of all study autonomous locomotory movements which stand in 

 close relation to the autonomous curvatures considered in the last lecture ; 

 induced locomotory phenomena will be treated of in the next lecture. 



Autonomous locomotory movements are exhibited by the protoplasts of 

 almost all plants, but they are naturally limited in extent by the rigid cell-walls. 

 In many lower organisms, on the other hand, these movements are not so cir- 

 cumscribed, for such organisms have the power of creeping over the substratum 

 or of swimming through the watery medium in which they live. We will take 

 the latter case first. 



Natatory movements occur in many Flagellata, very lowly organisms which 

 may with equal accuracy be classified either among plants or among animals. 

 These movements may continue during the entire life-history of the organism. 

 In Algae, Fungi, and Bacteria, certain cells, at least temporarily, possess the 

 power of locomotion ; such cells are known as swarmspores or zoospores, and 

 their function is to carry out asexual propagation and thus conduce, more espe- 

 cially, to the wide distribution of the species concerned. Further, the sexual 

 cells are frequently adapted to a motile existence, both male and female cells 

 among the lower forms having that power, while among more highly developed 

 types motility is confined to the male cell. Motile sperms occur not only among 

 mosses and ferns, but the corresponding cells even in Gymnospermae may exhibit 

 the same characteristic (of motility) more or less distinctly. All such motile 

 cells are provided with filamentous appendages, flagella, or cilia, whether they 

 be surrounded by cell-walls (Bacteria, Flagellata) or not (swarmspores, sperms). 

 These cilia effect the movement of the cell-body by rapid bendings, beating the 

 water and driving the cell forwards, as a boat is propelled by its oars. They 

 are developed from the ectoplasm and are themselves protoplasmic in character. 

 In order to carry out their function they must be surrounded by water, into 

 which they project through pores in the cell-membrane. As a general rule 

 alterations in form do not come under consideration in natatory movements. 



Let us take as our first example of an organism propelled by cilia the swarm- 

 spores of Algae (Nagelj, i860). The swarmspores are naked, and formed, 

 several at a time, in a mother-cell, and each exhibits all the essential constituents 



